Osteoclast Activity around Loaded and Unloaded Implants; an Histological Study in the Beagle Dog

Objective: the mechanisms of bone loss around dental implants are poorly understood. The osteoclast is the most important bone resorbing cell. Humoral factors seem able to stimulate the differentiation of osteoclasts from mononuclear phagocytes. Bacterial lipopolysaccharides seem to be directly involved in inflammatory bone loss by stimulation of the survival and fusion of preosteoclasts. Excessive load seems to be able to cause bone loss. Aim of the present work was an evaluation of the presence and number of osteoclasts in peri-implant bone in control (unloaded) and test (loaded) implants, to see if loading per se could be a contributing factor in peri-implant bone resorption. Methods: the protocol was approved by the Ethical Committee of Madrid University. Forty-eight implants were inserted in the mandibles of 4 beagle dogs. After 3 months, a prosthetic superstructure was inserted on 24 implants, while, on the contrary, on 24 implants only the healing screws were positioned. Twenty-four implants (12 test and 12 control) were retrieved at 6 months, and 24 implants (12 test and 12 control) were retrieved at 12 mnths. All implants were osseointegrated. Results: the number of osteoclasts found in the crestal bone in the first 3 mm from the implant surface was evaluated. The mean number of osteoclasts was: 1) control implants (6 months) 5.66 +/- 0.81 2) control implants (12 months) 2.55 +/- 1.05 3) test implants (6 months) 5.25 +/- 1.55 4) test implants (12 months) 2.5 +/- 1.0 No statistically significant differences were observed between the control and test implants. Conclusion: according to our data, loading per se does not seem to have a relevant importance on the osteoclast activation in peri-implant bone.